View of a small village in a valley in the Alps.
© Getty Images

Building and buying

Combined heat and power units: functioning, planning and costs

Thomas Bott

A combined heat and power unit (CHP) is a small power station for your own house. First and foremost, this ensures independence, as it generates not only heat for heating – but also hot water and electricity. In Switzerland, this type of system is still rarely used, especially in single-family houses. Find out here how a combined heat and power unit works and what needs to be taken into account during the planning stage. You will also discover whether it is economical, how much it costs and where the advantages and disadvantages lie.

A simple guide to combined heat and power units

Diesel generators, for example on trailers, are familiar to many people. This type of system consists of a diesel engine that drives a generator, which then generates electricity from kinetic energy. A combined heat and power unit works on a similar principle. Here too, a motor drives a generator, and the system produces electricity. What makes a CHP different, however, is that it makes use of the energy that would otherwise be lost.

Combustion in the motor generates heat, which the generator otherwise simply releases into the environment. In a combined heat and power unit, the heat from the cooling water and the exhaust gases is transferred via a heat exchanger to the heating circuit and the process water. It therefore involves cogeneration of combined heat and power. By putting fuel into the CHP, in the end you obtain electricity, heating and hot water. This makes the combined heat and power unit very efficient – especially in comparison to other heating systems.

A heating control on a wall. In the background a kitchen can be seen with two people in it.

Don’t worry about keeping the heat on: you should make as much use as possible of the energy generated by your own combined heat and power unit.

Planning: what to consider when installing a CHP

Good planning is particularly important when envisaging the installation of a combined heat and power unit, as it will determine whether the technology will pay off for you. The key factor is the existing situation. Ideally, you should know exactly what your heating requirements are, how well the building is insulated, how much electricity is consumed annually and how much hot water is used. This data can be extremely useful to a specialist during the planning phase.

It is also important that there are no other systems in the building that generate heating energy or electricity. A CHP is worthwhile if you use heat and electricity yourself to the greatest possible extent. If you already have an idea of your preferred energy source and the appropriate motor technology, this will also be a great help when planning your system.

Motors and energy sources: an important decision

Although combined heat and power units always work according to the same basic principle, they are available in different designs. The main factor is the fuel used. This determines which type of motor will be incorporated into the CHP and the overall environmental impact of the system. Combined heat and power (CHP) units work with fossil fuels such as:

  • Fuel oil
  • Natural gas

Alternatively, they can be operated with renewable energies. This reduces CO2 emissions, resulting in a lower environmental impact. Systems are currently available that work with the following fuels:

  • Biogas
  • Plant oils
  • Wood

Rapeseed oil is often used as a plant oil. There is also a wide variety of firewood available on the market, including pellets, logs, wood chips and briquettes. Individual materials differ in terms of the cleanliness of their combustion, and their cost varies significantly.

A man holds up a big bag of wood pellets to the camera.

Wood pellets are a sustainable and relatively environmentally friendly way of operating a combined heat and power unit.

Costs: what to expect for a CHP

A combined heat and power unit entails high investment costs. For private households, nano-, micro- or mini-cogeneration is possible. Depending on the design and energy requirements of the system, it will cost between 15,000 and 50,000 francs to purchase. By way of comparison, oil heating costs around 10,000 francs, and gas heating is available from 6,000 francs. However, when choosing a CHP, it’s important to choose a smaller unit with a long service life rather than an overly large unit with a short service life. The complexity of the installation and costs that could be incurred for conversion work depend entirely on the building.

The cost of buying fuel should also be integrated into the calculation, although it is difficult to calculate a fair average, as fuel prices fluctuate a great deal. If you decide on oil heating, for example, you must also factor in the tank. For gas heating you will need a connection, while wood takes up a considerable amount of space.

However, the calculation should also take into account the fact that you can earn money with a CHP system. The excess electricity flows into the grid, and you will receive remuneration for it. This has a positive effect on the profitability of CHP units.

Combined heat and power units: advantages and disadvantages at a glance

  • Advantages
  • Disadvantages
  • A CHP unit produces heat, hot water and electricity at the same time.
  • High acquisition cost of a CHP unit.
  • You are not dependent on external suppliers.
  • A lot of space is usually required for the storage of the chosen fuel.
  • The efficiency of the system is significantly higher than that of a simple oil or gas heating system, for example.
  • Fluctuating prices for purchasing fuel.
  • The system has a low environmental impact, especially when using renewable energies as fuel.
  • Economic efficiency is greatly dependent on individual consumption.
  • Existing radiators can usually still be used.

Conclusion: more independence thanks to a combined heat and power unit

Heat for water and heating as well as electricity can be generated by a combined heat and power unit in your own house. This means you are not dependent on an external energy supply. You are still reliant on suppliers to obtain the necessary fuel, however. Whether a CHP is worthwhile for you depends entirely on the unit and your needs. Consequently, it’s very important to consult a specialist for advice.

Read next

On our website we use cookies and analysis tools to constantly improve user-friendliness. This allows us to offer you the best possible service and personalize the advertising for you, both on our website and with our advertising partners. By using the website, you agree to the use of cookies. You can find more detailed provisions in our Privacy Statement).